Controlling reverse current in switched mode power supplies to achieve zero voltage switching

Abstract

A switched mode power supply includes a multilevel buck power converter and a control circuit. The power converter includes a first buck circuit and a second buck circuit each having a power switch, a rectifier, and an inductor. The power supply may further include a resonant power converter coupled to the multilevel buck power converter. In some examples, the control circuit is configured to generate control signals for the first buck circuit's power switch and the second buck circuit's power switch to control the power converter, and adjust a switching frequency of the control signals to control the amount of reverse current flowing in the first buck circuit and the second buck circuit to achieve zero voltage switching of the first buck circuit's power switch and the second buck circuit's power switch. Other example multilevel buck power converters and power supplies are also disclosed.

The invention claimed is: 
     
       1. A switched mode power supply comprising:
 a power converter comprising:
 a first buck circuit comprising a power switch; and 
 a second buck circuit comprising a power switch; and 
 
 a control circuit coupled to the first buck circuit and the second buck circuit, the control circuit configured to generate a first control signal for the power switch of the first buck circuit and a second control signal for the power switch of the second buck circuit to control the power converter; 
 wherein the control circuit is configured to adjust a switching frequency of the first control signal and the second control signal to control an amount of a reverse current flowing in the first buck circuit and the second buck circuit to achieve zero voltage switching of the power switch of the first buck circuit and the power switch of the second buck circuit while the power converter is in its continuous conduction mode; and 
 wherein the first control signal and the second control signal have overlapping on times when a duty cycle of the first control signal and the second control signal exceeds a duty cycle threshold value, and non-overlapping on times when the duty cycle of the first control signal and the second control signal is below the duty cycle threshold value. 
 
     
     
       2. The switched mode power supply of  claim 1 , wherein the first buck circuit further comprises a rectifier and an inductor; and
 wherein the second buck circuit further comprises a rectifier and an inductor. 
 
     
     
       3. The switched mode power supply of  claim 1 , wherein the switched mode power supply further comprises a resonant power converter coupled to an output of the power converter. 
     
     
       4. The switched mode power supply of  claim 3 , wherein the resonant power converter includes an interleaved resonant power converter. 
     
     
       5. The switched mode power supply of  claim 3 , wherein the resonant power converter is operated at a fixed switching frequency. 
     
     
       6. The switched mode power supply of  claim 1 , wherein the duty cycle threshold value is fifty percent. 
     
     
       7. The switched mode power supply of  claim 1 , wherein the control circuit is configured to:
 monitor the reverse current flowing in the first buck circuit and the second buck circuit; and 
 adjust the switching frequency of the first control signal and the second control signal in steps based on a value of the reverse current. 
 
     
     
       8. The switched mode power supply of  claim 1 , wherein the control circuit is configured to decrease the switching frequency of the first control signal and the second control signal to increase the amount of the reverse current flowing in the first buck circuit and the second buck circuit. 
     
     
       9. The switched mode power supply of  claim 1 , wherein the control circuit is configured to adjust the switching frequency of the first control signal and the second control signal when a load current of the switched mode power supply is in a defined range. 
     
     
       10. The switched mode power supply of  claim 9 , wherein the defined range includes 10% to 40% of a full load peak current of the switched mode power supply. 
     
     
       11. The switched mode power supply of  claim 9 , wherein the first control signal and the second control signal have:
 a first fixed switching frequency in response to the load current of the switched mode power supply being above the defined range; and 
 a second fixed switching frequency in response to the load current of the switched mode power supply being below the defined range. 
 
     
     
       12. A method of controlling a switched mode power supply for powering a load, the method comprising:
 generating, via a control circuit coupled to first and second buck circuits of a power converter, a first control signal for a power switch of the first buck circuit and a second control signal for a power switch of the second buck circuit to control the first and second buck circuits in a continuous conduction mode so that a reverse current flows in the first and second buck circuits; and 
 adjusting a switching frequency of the first and second control signals to control an amount of the reverse current flowing in the first and second buck circuits to achieve zero voltage switching of the power switches of the first and second buck circuits while the power converter is in its continuous conduction mode; and 
 wherein generating the first and second control signals comprises:
 generating the first control signal and the second control signal to have overlapping on times in response to a duty cycle of the first control signal and the second control signal exceeding a duty cycle threshold value; and 
 generating the first control signal and the second control signal to have non-overlapping on times in response to the duty cycle of the first control signal and the second control signal being below the duty cycle threshold value. 
 
 
     
     
       13. The method of  claim 12 , wherein the duty cycle threshold value is fifty percent. 
     
     
       14. The method of  claim 12  further comprising:
 monitoring the reverse current flowing in the first and second buck circuits; and 
 adjusting the switching frequency of the first control signal and the second control signal in steps based on a value of the reverse current. 
 
     
     
       15. The method of  claim 12  further comprising decreasing the switching frequency of the first control signal and the second control signal to increase the amount of the reverse current flowing in the first and second buck circuits. 
     
     
       16. The method of  claim 12  further comprising adjusting the switching frequency of the first control signal and the second control signal in response to a load current of the switched mode power supply being within a defined range. 
     
     
       17. The method of  claim 16 , wherein the defined range includes 10% to 40% of a full load peak current of the switched mode power supply. 
     
     
       18. The method of  claim 16 , wherein generating the first and second control signals comprises:
 generating the first and second control signals to have a first fixed switching frequency in response to the load current of the switched mode power supply being above the defined range; and 
 generating the first and second control signals to have a second fixed switching frequency in response to the load current of the switched mode power supply being below the defined range. 
 
     
     
       19. A method of controlling a switched mode power supply for powering a load, the method comprising:
 generating, via a control circuit coupled to first and second buck circuits of a power converter, a first control signal for a power switch of the first buck circuit and a second control signal for a power switch of the second buck circuit to control the first and second buck circuits in a continuous conduction mode so that a reverse current flows in the first and second buck circuits; 
 adjusting a switching frequency of the first and second control signals to control an amount of the reverse current flowing in the first and second buck circuits to achieve zero voltage switching of the power switches of the first and second buck circuits while the power converter is in its continuous conduction mode; and 
 adjusting the switching frequency of the first control signal and the second control signal in response to a load current of the switched mode power supply being within a defined range; 
 wherein generating the first and second control signals comprises:
 generating the first and second control signals to have a first fixed switching frequency in response to the load current of the switched mode power supply being above the defined range; and 
 generating the first and second control signals to have a second fixed switching frequency in response to the load current of the switched mode power supply being below the defined range.